The station reports that in an email to Contra Costa County officials, Phillips 66 representatives said the leak, which released 25 to 50 gallons of gas oil into San Pablo Bay at the Carquinez Strait, in Rodeo, “is believed to have been caused by localized corrosion.”

The spill took place Monday, Sept. 4, at Phillips 66's Rodeo, California, refinery.

The company did not immediately respond to a request for further information Monday (Sept. 11).

400-Square-Foot Sheen

According to the San Francisco CBS affiliate, the spill was discovered around 8:15 last Monday morning (Sept. 4). The release of oil was quickly stopped, but not before a sheen about 20 feet by 20 feet spread onto the water.

The state’s Office of Spill Prevention and Response, part of the Department of Fish and Wildlife, reported from the scene that there were no visibly oiled wildlife spotted.

FRT respond to spill in Carquinez Strait. Pipeline leak found and stopped. Report no sign of oil on shoreline or visibly oiled wildlife. pic.twitter.com/VtkUif5UbZ

According to state documentation, investigations are still ongoing, and an official cause has not been determined.

Past Spill

The same Phillips 66 refinery was the site of another sheen in September 2016, which was attributed to a transfer of oil from a tanker to the refinery at the marine terminal. Phillips 66 and the ship owner were held responsible for that release, according to the U.S. Coast Guard, but the exact cause was not determined. A number of people fell ill in nearby Vallejo due to a strong odor the same day, and the spill was “likely” the source of the odor, according to state officials.

Phillips 66 has two Bay Area refineries—Rodeo and Santa Maria, in Arroyo Grande, connected by a 200-mile pipeline. The Rodeo refinery was built in 1896, according to the company. In addition to the pipeline, the refineries move product via railcar and ship.